Thermal processing furnace, gas delivery system therefor, and methods for delivering a process gas thereto

ABSTRACT

A gas delivery system for supplying a process gas from a gas supply to a thermal processing furnace, a thermal processing furnace equipped with the gas delivery system, and methods for delivering process gas to a thermal processing furnace. The gas delivery system comprises a plurality of regulators, such as mass flow controllers, in a process gas manifold coupling a gas supply with a thermal processing furnace. The regulators establish a corresponding plurality of flows of a process gas at a plurality of flow rates communicated by the process gas manifold to the thermal processing furnace. The gas delivery system may be a component of the thermal processing furnace that further includes a liner that surrounds a processing space inside the thermal processing furnace.

FIELD OF THE INVENTION

This invention relates to the field of semiconductor processing, and,more particularly, to gas delivery systems for a thermal processingfurnace, thermal processing furnaces with a gas delivery system, andmethods for delivering a process gas to a thermal processing furnace.

BACKGROUND OF THE INVENTION

Thermal processing furnaces are commonly used to perform a variety ofsemiconductor fabrication processes, including but not limited tooxidation, diffusion, annealing, and chemical vapor deposition (CVD).Most conventional thermal processing furnaces typically employ aprocessing chamber that is oriented either horizontally or vertically.Vertical thermal processing furnaces generate fewer particles duringprocessing, which reduces substrate contamination, are readilyautomated, and require less floor space because of their relativelysmall footprint.

One common application of thermal processing furnaces is the growth ofhigh-quality thin dielectric layers during integrated circuitmanufacture to provide, among other uses, device isolation, transistorgate dielectrics and capacitor dielectrics. Dielectric layers of silicondioxide grown by conventional wet or dry thermal oxidation processesexhibit reduced quality and long-term reliability as the thickness isreduced. Oxidation of silicon in an ambient containing nitrous oxide(N₂O) is recognized as a means for improving the quality of silicondioxide dielectric layers, as compared to those grown via conventionaldry or wet oxidation processes. The increased reliability of suchdielectric layers may result from the incorporation of nitrogen atomsoriginating from the nitrous oxide into the silicon dioxide matrix toform a silicon oxynitride. After a thin layer of silicon oxynitrideforms on the surface, the diffusion of oxidant species to the underlyingsilicon is greatly hampered. Thus, the resultant dielectric layers grownusing a process gas containing nitrous oxide are thin. Other benefitsaccrue from the use of silicon oxynitride as a dielectric, such assuperior diffusion barrier properties for certain common dopant specieslike boron used in semiconductor device fabrication.

When using nitrous oxide as a process gas for forming silicon oxynitridedielectrics, a problem that is encountered is process matching or therepeatability of a process among different tools when exactly the sameprocess and hardware configuration is used. The outcome is differentprocess results (e.g., thickness for the oxynitride layer and thenitrogen profile in the oxynitride layer) among different thermalprocessing furnaces. To increase throughput, a typical process lineincludes multiple thermal processing furnaces. Achieving processuniformity among the different thermal processing furnaces is desiredbut, unfortunately, rarely achieved.

One attribute of conventional hardware configurations is that the flowof nitrous oxide to the process chamber is regulated or metered by amass flow controller. The delivery line transporting the metered nitrousoxide flow is divided at a common point in the gas manifold downstreamfrom the mass flow controller. The divided metered nitrous oxide flow isconveyed to a pair of gas injectors, which inject the nitrous oxideprocess gas inside the process chamber for forming silicon oxynitridelayers on the substrates held inside the process chamber. Uponinjection, the nitrous oxide spontaneously undergoes an exothermicreaction that decomposes or cracks the nitrous oxide molecules to formnitric oxide (NO) and other reaction by-products (e.g., O₂, N₂), whichreact with the substrates to grow the oxynitride layer.

The gas injectors for thermal processing furnaces are hand manufacturedfrom a length of dielectric tubing to specific dimensional tolerancesthat are predetermined according to the hardware configuration of thethermal processing furnace. Minor deviations from targeted manufacturingtolerances often result in a set of gas injectors that exhibits anasymmetrical or non-symmetric flow ratio among the individual gasinjectors. Attempts to manufacture different sets of gas injectors toidentical dimensional tolerances so as to exhibit identicalnon-symmetric flow ratios as a master set of gas injectors is difficult,if not impossible.

The flow ratio of the nitrous oxide injected into the process chamber isan important parameter in determining the reaction by-products of thecracking or decomposition. A variation in the flow rate ratio may causea significant change in the nitrogen content and profile in theoxynitride layer and/or a significant change in the layer thickness.Because of the inability to manufacture dimensionally matched sets ofgas injectors, significant differences in the properties of theoxynitride layer may be apparent for the same intended process executingon different conventional thermal processing furnaces, which isunacceptable.

There is thus a need for an improved apparatus and method forcontrolling the cracking of nitrous oxide in a thermal processingfurnace that overcomes these and other disadvantages of the apparatusand methods currently used in conventional thermal processing furnaces.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a gas delivery systemfor supplying a process gas from a gas supply to a thermal processingfurnace. The gas delivery system comprises a process gas manifoldadapted to couple the gas supply with the thermal processing furnace andfirst and second regulators, which may advantageously be mass flowcontrollers, each coupled with the process gas manifold between the gassupply and the thermal processing furnace. The first regulatorestablishes a first flow rate of a first flow of the process gascommunicated by the process gas manifold to the thermal processingfurnace. The second regulator establishes a second flow rate of a secondflow of the process gas communicated by the process gas manifold to thethermal processing furnace. In certain embodiments of the presentinvention, the gas delivery system may be a component of the thermalprocessing furnace that further includes a liner surrounding aprocessing space inside the thermal processing furnace in which thesubstrates are processed with the process gas.

In another embodiment, the thermal processing furnace may comprise afurnace tube having a substrate processing space and first and secondgas injectors positioned inside the furnace tube. The first gas injectorincludes a first outlet positioned for injecting a first flow of theprocess gas into the processing space. Similarly, the second gasinjector includes a second outlet positioned for injecting a second flowof the process gas into the processing space. The thermal processingfurnace further comprises a first regulator coupled in fluidcommunication with the first gas injector and a second regulator coupledin fluid communication with the second gas injector. The first regulatoris configured to control a first flow rate of the process gas to thefirst gas injector. The second regulator is configured to control asecond flow rate of the process gas to the second gas injector.

In another embodiment, a method is provided for processing substrateswith a process gas in a processing space inside, for example, a thermalprocessing furnace. The method comprises branching a flow of the processgas to establish a first stream and a second stream, metering the firststream of the process gas to establish a first mass flow rate, andmetering the second stream of the process gas to establish a second massflow rate. The method further comprises injecting the first and secondstreams of the process gas into the processing space at the respectivefirst and second mass flow rates and combining the first and secondstreams of the process gas inside the processing space.

In yet another embodiment, a method is provided for controlling aprocess for growing an oxynitride layer with a nitrogen content on asubstrate. The method comprises injecting first and second gas streamseach containing nitrous oxide at a flow rate ratio into a processingspace, exposing the substrate held in the processing space to theplurality of gas streams, and heating the substrate to a processtemperature adequate to grow the oxynitride layer on the substrate. Themethod further comprises changing the flow rate ratio between the firstand second gas streams to alter the nitrogen content in the oxynitridelayer without changing the process temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIG. 1 is a diagrammatic view of a thermal processing furnace of thepresent invention.

FIG. 2 is a side view in partial cross section of a thermal processingfurnace of the present invention.

FIG. 3 is a detailed view of a first portion of FIG. 2.

FIG. 4 is a detailed view of a second portion of FIG. 2.

FIG. 5 is a top view in partial cross section of the thermal processingfurnace of FIG. 2 taken generally along line 5-5 from FIG. 2.

FIG. 6 is a detailed view of a portion of FIG. 5.

DETAILED DESCRIPTION

With reference to FIG. 1, a process tool in the form of a thermalprocessing furnace 10 comprises a furnace tube or outer housing 12 thatsurrounds a processing compartment or space 26 adapted to receive abatch of substrates 36 (FIG. 2). The thermal processing furnace 10utilizes the process gas supplied from a gas supply 14, such as a gascylinder of compressed process gas, for growing a layer on a batch ofsubstrates 36 in the controlled atmosphere ambient of the processingspace 26 that contains a partial pressure of a process gas. Morespecifically, the thermal processing furnace 10 may be used for thermaloxidation of silicon substrates 36 in a controlled atmosphere ambientcontaining a process gas such as, for example, nitrous oxide (N₂O) toincorporate nitrogen atoms originating from the nitrous oxide into asilicon dioxide matrix to form a silicon oxynitride layer on a batch ofsemiconductor substrates 36. The invention contemplates that the processtool constituting the point of use for the process gas may comprise adifferent type of processing apparatus. In any event, the process gassupplied from the gas supply 14 is typically electronics grade inpurity.

The gas supply 14 is coupled in fluid communication with a pair ofregulators, represented by mass flow controllers 16, 18, by a deliveryline 20 of a gas manifold 25. At a branch site 19 upstream from the massflow controllers 16, 18, the delivery line 20 is bifurcated into twoseparate branch delivery lines 20 a,b. A portion of the process gasflowing in delivery line 20 is diverted into each of the branch deliverylines 20 a,b at the branch site 19. As a result, each of the mass flowcontrollers 16, 18 receives an independent stream of process gas fromthe gas supply 14. Of course, the delivery line 20 may be split amongmore than two branch delivery lines, similar to branch delivery lines 20a,b, if additional mass flow controllers (not shown) are added to thegas manifold 25. The gas manifold 25 advantageously solves many of thedeficiencies of conventional gas manifolds for thermal processingsystems constructed similar or identical to thermal processing system10.

A delivery line 22 of the gas manifold 25 communicates a flow of processgas from mass flow controller 16 to a gas injector 24 in the form of aconduit stationed inside the thermal processing furnace 10 that injectsthe flow into the processing space 26 defined inside the outer housing12. Another delivery line 28 of the gas manifold 25 communicates a flowof process gas from mass flow controller 18 to another gas injector 30in the form of a conduit stationed inside the thermal furnace 10 thatlikewise injects the flow inside the processing space 26. The twodelivery lines 22, 28 define independent flow paths from the gas supply14 to the thermal processing furnace 10.

The mass flow controllers 16, 18 are closed loop devices that set,measure, and control the flow of the process gas to the gas injectors24, 30, respectively. To that end, the mass flow controllers 16, 18include a mass flow sensor and a valve that meters and controls the rateof flow of gas in response to control signals generated by circuitryinterfaced with, and receiving mass flow measurements from, the massflow sensor. Although the invention is not so limited, the mass flowcontrollers 16, 18 may comprise 30 standard cubic centimeters per minute(sccm) mass flow controllers.

The mass flow controllers 16, 18 regulate and control the flow rate ofprocess gas in each of the delivery lines 22, 28 such that the flowrates in the delivery lines 22, 28 from the gas supply 14 to the gasinjectors 24, 30 are independently controlled. The result is that therelative flow rates of the process gas injected from the two gasinjectors 24, 30 at the corresponding injection points inside thethermal processing furnace 10 are independently controlled by the massflow controllers 16, 18. Advantageously, the independent control overthe flow rates of process gas injected by the gas injectors 24, 30represents a significant improvement over conventional gas manifoldsthat split or divide a single mass-flow controlled process gas stream toconventional injectors inside a thermal furnace.

The delivery lines 20, 22, 28 and the gas injectors 24, 30 are openended conduits or tubing having a sidewall with inner and outerdiameters that surrounds a lumen through which the process gas flows.Conventional couplings are used to establish fluid connections. Thecontrol over the individual flow rates is achieved without regard to theconfiguration (length, geometry, etc.) of the individual delivery lines20, 22, 28 and gas injectors 24, 30. The delivery lines 20, 22, 28 arecommonly manufactured from stainless steel and the gas injectors 24, 30are commonly formed from a ceramic like quartz.

With reference to FIGS. 2-6, a wafer boat 32 is disposed inside thethermal processing furnace 10 and is supported on a pedestal 34. Thewafer boat 32, which is typically composed of quartz, includes aplurality of open slots that accommodate a corresponding plurality ofsubstrates 36. The open slots in the wafer boat 32 are spaced apart suchthat unreacted process gas is readily available to react with thesubstrates 36. Unprocessed substrates 36 are inserted into the slots ofwafer boat 32 and processed substrates 36 are removed from the slots bya robotic wafer handler (not shown). The pedestal 34 is coupled to aboat elevator (not shown) for inserting and removing the wafer boat 32.

The process chamber 12 includes a process tube or liner 38 that has adomed ceiling 40 and an opposed open end 42 that is sealed with a baseplate (not shown). The wafer boat 32 and substrates 36 are disposedinside the liner 38 generally between the domed ceiling 40 and open end42 of the liner 38, which peripherally bounds the processing space 26.The dimensions of the liner 38, and thus the size of the thermalprocessing furnace 10, may be scaled to accommodate substrates 36 ofdifferent sizes. The liner 38 may be composed of any high temperaturematerial, such as quartz, silicon carbide, and another suitable ceramicmaterial, and is removable for cleaning to remove accumulated depositsthat are an artifact of substrate processing.

A suitable heating element (not shown) is positioned outside of theouter housing 12 and operates to elevate the temperature of the liner 38by heat transfer so that the processing space 26 is surrounded by a hotwall during substrate processing. For example, the heating element maycomprise a cylindrical shaped heating element that surrounds theexterior of the outer housing 12. The heating element may be dividedinto a plurality of heating zones each having an independent powersource for controlling the corresponding zone temperature. Temperaturesensors (not shown), such as thermocouples, are stationed along theheight of the liner 38 and provide temperature information for thedifferent heating zones. The temperature sensors supply feedback used bya temperature controller (not shown) to regulate the monitoredtemperature of the liner 38 in each of the heating zones. Typically, thezone temperatures are regulated to provide a flat or isothermaltemperature profile for the liner 38 at a target temperature specifiedfor the process, which is typically in the range of 800° C. to 1200° C.and, more typically, in the range of 900° C. to 1000° C. The temperaturecontroller may employ, for example, a proportional integral derivative(PID) algorithm to determine the power applied to each zone of theheating element based upon the error between the monitor and targettemperatures.

Delivery line 22 from the mass flow controller 16 is routed to a fluidfeedthrough 44 mounted to a port in the liner 38 near a base 46 of thethermal processing furnace 10. The delivery line 22, which is commonlymade of a stainless steel, is transitioned in the feedthrough 44 tocommunicate with gas injector 24, which is commonly formed from aceramic like quartz. Delivery line 28 is likewise transitioned through afeedthrough (not shown) to communicate with gas injector 30. In thismanner, the process gas is transferred to the interior of the liner 38.

Gas injector 24 has a stem portion 47 that enters the liner 38horizontally, as best shown in FIG. 3, via fluid feedthrough 44 andbends in a near right angle 48 to define a vertical portion 50positioned between the liner 38 and wafer boat 32. The vertical portion50 provides a vertical rise that extends proximate to a curved,inwardly-facing surface 38 a of the liner 38, as best shown in FIG. 6.The proximity of the vertical portion 50 to the liner 38 rapidly heatsthe process gas flowing through the gas injector 24 above thetemperature, typically room temperature, at entry into the thermalprocessing furnace 10.

Near the domed ceiling 40 of liner 38, an angled bend 52 redirects thegas injector 24 to define a radial segment 54 that extends in ahorizontal run generally toward an azimuthal axis 56 of the liner 38. Ata location near the azimuthal axis 56 and as best shown in FIG. 4, thegas injector 24 bends in at an angled bend 58 to define a short verticalportion 60 extending toward the domed ceiling 40. An injection port oroutlet 62 is defined at the free end or tip of the gas injector 24 andthe vertical portion 60 is oriented such that the process gas exitingthe outlet 62 is directed generally toward domed ceiling 40. The outlet62 is spaced from the domed ceiling 40.

Gas injector 30 has a construction similar to gas injector 24 thatincludes a vertical portion (not shown) similar to the vertical portion50 of gas injector 24. The gas injector 30 includes a radial segment 64and an angled bend 66 connecting the radial segment to a verticalportion 68. The vertical portion 68 extends toward the domed ceiling 40of liner 38 and terminates at an injection port or outlet 70 defined atthe tip of the gas injector 30. The outlet 70 of gas injector 30 ispositioned adjacent to the outlet of gas injector 24 near the domedceiling 40 of liner 38. In exemplary embodiments, the gas injectors 24,30 have an inner diameter of 5 mm to 6 mm defining the fluid lumen andan outer diameter of about 8 mm so that the wall thickness is between 2mm and 3 mm, equal diameter outlets 62, 70 that are equidistant from thenearest portion of the domed ceiling 40, and the center-to-centerdistance, S, between centerlines 61, 71 of the outlets 62, 70 is lessthan about 20 mm and, advantageously, about 10 mm to about 20 mm.

The outlets 62, 70 may be located at approximately the same distancefrom the inner surface of the domed ceiling 40 or may be positioned withdifferent relative separations from the inner surface of the domedceiling 40. For gas injector 24, as an example, the positioning of theoutlet 62 may be varied by changing the length of the vertical portion60 and/or by changing the angles of the bends 52, 58. For gas injector24, as an example, the length of radial segment 54 will determine theseparation of the outlet 62 from the azimuthal axis 56.

The invention contemplates that additional gas injectors (not shown),each similar or identical to gas injectors 24, 30, may be located insidethe thermal processing furnace 10. These additional gas injectors may befed process gas originating from gas supply 14 and, thus, have a flowrate regulated by a corresponding mass flow controller (not shown)similar to mass flow controllers 16, 18. In this manner, the thermalprocessing furnace 10 may be equipped with a plurality of more than twogas injectors and process gas injection points.

Volatile reaction products and unreacted process gas are evacuated fromthe processing space 26 by a vacuum pump 72 (FIG. 1) through a vacuumport 74 near the base 46. During operation, the evacuation of theprocessing space 26 is continuous, as is the introduction of process gasvia gas injectors 24, 30.

In use and with reference to FIGS. 1-6, the process run is initiatedwith the liner 38 held at an idle temperature. The substrates 36 areloaded into the wafer boat 32 and the temperature of the liner 38 isramped up to the target process temperature. Process gas is directedthrough the mass flow controllers 16, 18 with individually controlledflow rates to the gas injectors 24, 30. Heat transferred from the liner38 heats the process gas over the vertical rise of the gas injectors 24,30 toward the domed ceiling 40 of liner 38. The heated process gas isinjected into the processing space 26 from the outlets 62, 70 of the gasinjectors 24, 30, respectively. The heated process gas, which mayexperience a reaction upon injection, flows downwardly toward the vacuumport 74 under the influence of the vacuum pump 72. The process gasand/or its reaction products may chemically react with the heatedsubstrates 36 to form a surface layer on each substrate 36. Unreactedprocess gas and volatile reaction products are evacuated from theprocessing space 26 through the vacuum port 74. After a given amount oftime at the process temperature sufficient to accomplish the desiredprocess, the process gas flow is discontinued, the liner 38 is cooledback to an idle temperature, and the processed substrates 36 areunloaded from the thermal processing furnace 10.

The present invention may be particularly advantageous if the injectedprocess gas is nitrous oxide. Specifically, nitrous oxide injected fromthe outlets 62, 70 of the gas injectors 24, 30 experiences an exothermicreaction that decomposes or cracks the nitrous oxide molecules to formnitric oxide (NO) and other reaction by-products (e.g., O₂, N₂). Thenitrous oxide decomposition is believed to predominantly occur beforethe flow reaches the substrates 36 held by the boat 32. A primary factorthat influences the relative amounts of reaction by-products formed bynitrous oxide cracking is the peak gas temperature near the point ofinjection. The spontaneous exothermic reaction experienced by thenitrous oxide increases the gas temperature. Without wishing to belimited by theory, the magnitude of temperature increase is believed todepend, among other things, on the process temperature and the nitrousoxide flow rate. Silicon substrates 36 exposed to the decomposed nitrousoxide will grow a surface layer of oxynitride that may be represented bythe chemical formula Si_(x)O_(y)N_(z). The chemical structure andcomposition, including the uniformity of the distribution of nitrogenthroughout the oxynitride thin film, may vary depending on the processconditions.

In accordance with the invention, the peak gas temperature of thearriving nitrous oxide may be advantageously controlled or modulated byindependently selecting the flow rates of nitrous oxide to each of thegas injectors 24, 30 using the mass flow controllers 16, 18. Theselection of the individual flow rates assigns a precise ratio to thegas velocity for the injected flows of nitrous oxide, which determinesthe nature of the nitrous oxide flow field near the outlets 62, 70 ofthe gas injectors 24, 30 and at the domed ceiling 40 of the liner 38.The flow field from the interaction of the individual flows influencesthe temperature distribution of the arriving nitrous oxide, whichcontrols the amounts of nitric oxide and other reaction by-products(e.g., O₂, N₂) resulting from the nitric oxide decomposition andultimately influences the characteristics of the oxynitride thin filmsformed on the substrates 36.

The present invention advantageously allows for a universal hardwareconfiguration with two mass flow controllers 16, 18 in which the nitricoxide production from the nitrous oxide may be varied while holding thesubstrates 36 at a single, fixed process temperature. A specific processmay be repeatable among different thermal processing furnaces 10 havingthe universal hardware configuration by regulating the decomposition ofthe nitric oxide using the independently adjustable gas flows. Thispermits better tool matching among different thermal processing furnaces10 of the invention. The ability to modulate the reaction by-productsfrom the nitric oxide cracking and, in particular, the amount of nitricoxide permits the nitrogen content in the oxynitride thin film to bevaried at any process temperature by merely changing the flow rate ratioamong the gas injectors 24, 30. In contrast, the sole recognizedtechnique for varying the nitrogen content in oxynitride thin films inconventional thermal processing furnaces is believed to be changing theprocess temperature, which unwantedly prompts a change in the oxidationprocess. The present invention permits the nitrogen content in theoxynitride thin films to be varied independent of the processtemperature or without changing the oxidation process. In other words,changing the flow rate ratio between the first and second gas streamsmay be used to alter the nitrogen content in the oxynitride layerwithout changing the process temperature or, stated differently, whilekeeping the process temperature constant.

The present invention is believed to permit the use of nitrous oxidechemistries at lower pressures and temperatures where incompletecracking of nitrous oxide would ordinarily not occur. Thus, nitrogenprofiles in silicon dioxide thin films may be produced that are outsidethe conventional window of operation for a hardware configuration thatlacks the ability to independently control the flow rate ratio among theindividual gas injectors.

The present invention offers a cost effective and simplified approachfor obtaining repeatable results in the production of oxynitride layersamong different thermal processing furnaces, each similar to thermalprocessing furnace 10. By independently metering the process gas streamto the individual gas injectors, the present invention is tolerant todimensional variations in the individual gas injectors. The presentinvention also permits dynamic adjustments to the nitrous oxide crackingto overcome any manufacturing variations in the delivery lines 22, 28and gas injectors 24, 30 of different thermal processing furnaces. Thepresent invention facilitates tool matching such that a process runningon one thermal processing furnace 10 may be more easily implemented onadditional thermal processing furnaces 10 with the result that theprocess is substantially identical among the different thermalprocessing furnaces 10.

The present invention also advantageously lowers the manufacturing costof the gas injectors 24, 30 because the manufacturing tolerances arerelaxed by the ability to individually regulate the flow rates. Thecharacteristics of conventional gas injectors must be matched at theexpense of tight and stringent manufacturing tolerances to providesatisfactory process uniformity among different thermal processingfurnaces. In accordance with the present invention, the individual flowrates in the gas injectors 24, 30 may be independently controlled tocompensate for hardware differences among the gas injectors 24, 30 and,thereby, advantageously adjusting the nitrous oxide cracking if thethermal processing furnace 10 is using nitrous oxide as a process gas.

In other embodiments, the present invention may be executed in otherhorizontal or vertical thermal processing furnaces or in rapid thermalprocessing (RTP) systems having gas injectors.

While the present invention has been illustrated by the description ofone or more embodiments thereof, and while the embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The invention in its broader aspects is thereforenot limited to the specific details, representative apparatus and methodand illustrative examples shown and described. Accordingly, departuresmay be made from such details without departing from the scope of thegeneral inventive concept.

1. A gas delivery system for supplying a process gas from a gas supplyto a thermal processing furnace having a processing space therein, thegas delivery system comprising: a process gas manifold adapted to couplethe gas supply with the thermal processing furnace; a first regulatorcoupled with said process gas manifold between the gas supply and thethermal processing furnace, said first regulator configured to control afirst flow rate of a first flow of the process gas communicated by saidprocess gas manifold to the processing space of the thermal processingfurnace; and a second regulator coupled with said process gas manifoldbetween the gas supply and the thermal processing furnace, said secondregulator configured to control a second flow rate of a second flow ofthe process gas communicated by said process gas manifold to theprocessing space of the thermal processing furnace.
 2. The gas deliverysystem of claim 1 wherein said first and second regulators comprise massflow controllers.
 3. The gas delivery system of claim 1 wherein saidprocess gas manifold further comprises: a delivery line disposed betweenthe gas supply and said first and second regulators, said delivery lineincluding a branch site at which said delivery line branches into afirst branch coupled in fluid communication with said first regulatorand a second branch coupled in fluid communication with said secondregulator.
 4. The gas delivery system of claim 1 wherein said processgas manifold further comprises: a first gas injector coupled in fluidcommunication with said first regulator and having a first outletpositioned inside the thermal processing furnace, said first gasinjector configured to inject the first flow of the process gas fromsaid first outlet into the processing space; and a second gas injectorcoupled in fluid communication with said second regulator and having asecond outlet positioned inside the thermal processing furnace, saidsecond injector configured to inject the second flow of the process gasfrom said second outlet into the processing space.
 5. The gas deliverysystem of claim 4 wherein said first outlet has a first centerline andsaid second outlet has a centerline, said first and second centerlinesbeing separated by less than about 20 millimeters.
 6. The gas deliverysystem of claim 4 wherein said process gas manifold further comprises: afirst delivery line disposed between said first regulator and thethermal processing furnace, said first delivery line coupling said firstinjector in fluid communication with said first regulator; and a seconddelivery line disposed between said second regulator and the thermalprocessing furnace, said second delivery line coupling said secondinjector in fluid communication with said second regulator.
 7. A thermalprocessing furnace for processing substrates with a process gas from agas supply, the thermal processing furnace comprising: a furnace tubeincluding a processing space in which the substrates are processed withthe process gas; a process gas manifold coupling the gas supply withsaid processing space; a first regulator coupled with said process gasmanifold between the gas supply and said furnace tube, said firstregulator configured to control a first flow rate of a first flow of theprocess gas communicated by said process gas manifold to said processingspace; and a second regulator coupled with said process gas manifoldbetween the gas supply and said furnace tube, said second regulatorconfigured to control a second flow rate of a second flow of the processgas communicated by said process gas manifold to said processing space.8. The thermal processing furnace of claim 7 wherein said first andsecond regulators comprise mass flow controllers.
 9. The thermalprocessing furnace of claim 7 wherein said process gas manifold furthercomprises: a delivery line disposed between the gas supply and saidfirst and second regulators, said delivery line including a branch siteat which said delivery line branches into a first branch coupled influid communication with said first regulator and a second branchcoupled in fluid communication with said second regulator.
 10. Thethermal processing furnace of claim 7 wherein said process gas manifoldfurther comprises: a first gas injector coupled in fluid communicationwith said first regulator and having a first outlet positioned insidethe thermal processing furnace, said first gas injector configured toinject the first flow of the process gas from said first outlet into theprocessing space; and a second gas injector coupled in fluidcommunication with said second regulator and having a second outletpositioned inside the thermal processing furnace, said second injectorconfigured to inject the second flow of the process gas from said secondoutlet into the processing space.
 11. The thermal processing furnace ofclaim 10 wherein said process gas manifold further comprises: a firstdelivery line disposed between said first regulator and the thermalprocessing furnace, said first delivery line coupling said firstinjector in fluid communication with said first regulator; and a seconddelivery line disposed between said second regulator and the thermalprocessing furnace, said second delivery line coupling said secondinjector in fluid communication with said second regulator.
 12. Thethermal processing furnace of claim 10 wherein said first outlet has afirst centerline and said second outlet has a centerline, said first andsecond centerlines being separated by less than about 20 millimeters.13. A thermal processing furnace for processing substrates with aprocess gas, the thermal processing furnace comprising: a furnace tubeincluding a processing space for the substrates; a first gas injectorpositioned inside said furnace tube, said first gas injector including afirst outlet positioned for injecting a first flow of the process gasinto said processing space; a second gas injector positioned inside saidfurnace tube, said second gas injector including a second outletpositioned for injecting a second flow of the process gas into saidprocessing space; a first regulator coupled in fluid communication withsaid first gas injector, said first regulator configured to control afirst flow rate of the process gas to said first gas injector; and asecond regulator coupled in fluid communication with said second gasinjector, said second regulator configured to control a second flow rateof the process gas to said second gas injector.
 14. The thermalprocessing furnace of claim 13 wherein said first and second regulatorscomprise mass flow controllers.
 15. The thermal processing furnace ofclaim 13 further comprising: a delivery line disposed between a gassupply and said first and second regulators, said delivery lineincluding a branch site at which said delivery line branches into afirst branch coupled in fluid communication with said first regulatorand a second branch coupled in fluid communication with said secondregulator.
 16. The gas delivery system of claim 13 wherein said processgas manifold further comprises: a first delivery line disposed betweensaid first regulator and the thermal processing furnace, said firstdelivery line coupling said first injector in fluid communication withsaid first regulator; and a second delivery line disposed between saidsecond regulator and the thermal processing furnace, said seconddelivery line coupling said second injector in fluid communication withsaid second regulator.
 17. The thermal processing furnace of claim 13wherein said first outlet has a first centerline and said second outlethas a centerline, said first and second centerlines being separated byless than about 20 millimeters.
 18. A method for processing substrateswith a process gas in a processing space, the method comprising:branching a flow of the process gas to establish a first stream and asecond stream; metering the first stream of the process gas to establisha first flow rate; metering the second stream of the process gas toestablish a second flow rate; injecting the first and second streams ofthe process gas into the processing space at the respective first andsecond mass flow rates; and combining the first and second streams ofthe process gas inside the processing space.
 19. The method of claim 18wherein the process gas comprises nitrous oxide and combining the firstand second streams further comprises: reacting the first and secondstreams of the nitrous oxide to form reaction by-products; and growing adielectric layer with a nitrogen content on the substrates in thepresence of the reaction by-products.
 20. The method of claim 18 furthercomprising: heating the first and second streams of the process gasbefore combining the first and second streams inside the processingspace.
 21. The method of claim 18 wherein metering the first mass flowfurther comprises: adjusting a first mass flow controller to establishthe first flow rate for the first stream.
 22. The method of claim 21wherein metering the second mass flow further comprises: adjusting asecond mass flow controller to establish the second flow rate for thesecond stream.
 23. The method of claim 18 wherein the process gas isnitrous oxide, and combining the first and second streams furthercomprises: controlling a peak temperature of the nitrous oxide insidethe processing space by changing at least one of the first flow rate orthe second flow rate.
 24. The method of claim 18 wherein injecting thefirst and second streams of the process gas further comprises: injectingthe first and second streams of the process gas into the processingspace from respective first and second outlets having a center-to-centerseparation of less than about 20 millimeters.
 25. A method ofcontrolling a process for growing an oxynitride layer with a nitrogencontent, the method comprising: injecting first and second gas streamseach containing nitrous oxide at a flow rate ratio into a processingspace; exposing a substrate held in the processing space to theplurality of gas streams; heating the substrate to a process temperatureadequate to grow the oxynitride layer on the substrate; and changing theflow rate ratio between the first and second gas streams to alter thenitrogen content in the oxynitride layer without changing the processtemperature.
 26. The method of claim 25 further comprising: metering thefirst gas stream of the nitrous oxide to establish a first flow ratebefore injection into the processing space; and metering the second gasstream of the nitrous oxide to establish a second flow rate beforeinjection into the processing space to provide the flow rate ratiorelative to the first flow rate.
 27. The method of claim 25 whereinchanging the flow rate ratio further comprises: adjusting a first massflow controller to change the first flow rate.
 28. The method of claim27 wherein changing the flow rate ratio further comprises: adjusting asecond mass flow controller to change the second flow rate.